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ext4: tune mballoc's default group prealloc size for bigalloc file systems

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The default group preallocation size had been previously set to 512
blocks/clusters, regardless of the block/cluster size.  This is
probably too big for large cluster sizes.  So adjust the default so
that it is 2 megabytes or 32 clusters, whichever is larger.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2011-09-09 19:02:51 -04:00
parent f975d6bcc7
commit 27baebb849
1 changed files with 16 additions and 2 deletions
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18
fs/ext4/mballoc.c
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@ -126,7 +126,8 @@
* list. In case of inode preallocation we follow a list of heuristics
* based on file size. This can be found in ext4_mb_normalize_request. If
* we are doing a group prealloc we try to normalize the request to
* sbi->s_mb_group_prealloc. Default value of s_mb_group_prealloc is
* sbi->s_mb_group_prealloc. The default value of s_mb_group_prealloc is
* dependent on the cluster size; for non-bigalloc file systems, it is
* 512 blocks. This can be tuned via
* /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in
* terms of number of blocks. If we have mounted the file system with -O
@ -2473,7 +2474,20 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
sbi->s_mb_stats = MB_DEFAULT_STATS;
sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
/*
* The default group preallocation is 512, which for 4k block
* sizes translates to 2 megabytes. However for bigalloc file
* systems, this is probably too big (i.e, if the cluster size
* is 1 megabyte, then group preallocation size becomes half a
* gigabyte!). As a default, we will keep a two megabyte
* group pralloc size for cluster sizes up to 64k, and after
* that, we will force a minimum group preallocation size of
* 32 clusters. This translates to 8 megs when the cluster
* size is 256k, and 32 megs when the cluster size is 1 meg,
* which seems reasonable as a default.
*/
sbi->s_mb_group_prealloc = max(MB_DEFAULT_GROUP_PREALLOC >>
sbi->s_cluster_bits, 32);
/*
* If there is a s_stripe > 1, then we set the s_mb_group_prealloc
* to the lowest multiple of s_stripe which is bigger than